The candidate (Simon Tran, D.M.D.) is presently pursuing a combined clinical/research program consisting of a certificate in Periodontology, a Ph.D. in Oral Biology, and a minor in Epidemiology. His goals are to learn to treat periodontal diseases and to develop molecular microbiological detection tests for the diagnosis and study of adult periodontitis. Research Plan: The most convincing evidence of periodontal pathogenicity accumulated to date suggests that Actinobacillus actinomycetemcomitans, Bacteroides forsythus, and Porphyromonas gingivalis are etiological agents in destructive periodontal disease. However, the microbial flora associated with sites showing attachment loss has been prospectively evaluated in only a few studies, and results were conflicting regarding the ability of any one microorganism to be predictive for the progression of periodontitis. A possible explanation for those conflicting results is that the subjects studied were those with the most advanced cases of periodontitis. The complex microflora of these severe periodontitis cases might not differentiate which bacterial species initiated disease or which species simply proliferate after disease progression. The candidate has access to stored plaque samples of a longitudinally-followed population, which has a low prevalence of periodontitis. This gives the ad vantage of longitudinal observations of early microbial changes in the development or progression of periodontitis. This population may help to definitively determine the role of A.actinomycetemcomitans, B.forsythus, and P.gingivalis as risk factors for periodontitis. The candidate has developed a sensitive and specific multiplex PCR-based assay for simultaneous detection of low levels of A.actinomycetemcomitans, B.forsythus, and P.gingivalis. This research will test the hypothesis that the persistent presence of these periodontal pathogens in periodontally healthy sites is a risk factor for the onset of clinical attachment loss. The answer to be found will guide our approach to the treatment and understanding of the pathogenesis of periodontal diseases associated with these three bacterial species. Key Words: Periodontal pathogens, epidemiology, PCR, 16S ribosomal RNA. multiplex PCR